This invention relates to a process for the removal of iron from iron-containing petroleum crudes, heavy hydrocarbonaceous residua or solvent deasphalted oils derived from crudes and residua, using hydroxo-carboxylic acids, especially citric acid, as sequestering or chelating agents. A few, but increasingly important, petroleum crude feedstocks and residua contain levels of iron which render them difficult, if not impossible, to process using conventional refining techniques. Specifically, the iron contaminant causing particular problems solved by this invention is in the form of non-porphyrin, organometallically-bound compounds. These species have been attributed to either naturally-occurring iron complexes or solubilized iron from corrosion and decay of iron bearing equipment which comes in contact with crude oils. One possible class of iron-containing compounds identified in particular is the iron naphthenates and their homologous series. These organo-iron compounds are not separated from the feedstock by normal desalting processes, and in a conventinnal refining technique they can cause the very rapid deactivation of hydroprocessing catalysts. Examples of feedstocks demonstrating objectionably high levels of iron compounds are those from the San Joaquin Valley in California. Generally, these crudes are contained in a pipeline mixture referred to as San Joaquin Valley crude or residuum.
The problems presented by these forms of iron in petroleum feedstocks and their necessity for removal has been known for some time, but the prior art contains few references specifically to their removal, especially by extraction methods similar to the present invention. Metals removal using organic compounds generally, however, has been addressed in the prior art, specifically for the removal of known metallic contaminants, which are ordinarily found in feedstocks as porphyrins, and other related organometallic compounds. These metal-containing porphyrins include nickel, vanadium, and/or copper.
In U.S. Pat. No. 3,052,627, Lerner, metals-contaminants are removed from crude petroleum feedstocks using a 2-pyrrolidone-alcohol mixture. In U.S. Pat. No. 3,167,500, Payne, metallic contaminants, such as metal-containing porphyrins, are removed from petroleum oils using a condensed polynuclear aromatic compound having a preferred C/H ratio and a molecular weight ordinarily called pitch binders. In U.S. Pat. No. 3,153,623, Eldib et al., selected commercially available organic compounds of high dielectric strength were added to assist in the electrically-directed precipitation of metals with polar organic compounds.
It has now been unexpectedly found that the iron-containing contaminants may be effectively removed from the feedstocks of the present invention by binding the iron compounds using hydroxo-carboxylic acids and their salts.